Michigan
Figure 1
Michigan experiences large seasonal changes in temperature, with warm, humid summers and cold winters. The Great Lakes play an important role in moderating the state’s climate, causing it to be more temperate and moist than other north-central states. The Lower Peninsula is bordered by Lake Michigan to the west and by Lakes Huron and Erie to the east; the Upper Peninsula, by Lake Superior to the north and Lakes Michigan and Huron to the east and south. The moderating effect is most evident along the shores, which are considerably warmer during the winter and cooler in the summer than more inland locations. For example, Lansing and Muskegon have similar latitudes but experience very different frequencies of hot and cold days. Lansing, located in the center of the state, averages 9.0 hot days and 6.9 very cold nights per year. In contrast, Muskegon, located along the western shore of Lake Michigan, averages only 3.4 hot days and 2.5 very cold nights. The moderating effects are even more striking along the shores of the colder waters of Lake Superior in the Upper Peninsula. Sault Ste. Marie averages only 1.4 hot days per year, and there have been only 11 warm nights since 1888.
Temperatures in Michigan have risen almost 3°F since the beginning of the 20th century (Figure 1). Temperatures in the 2000s have been higher than in any other historical period. The year 2012 was the hottest on record, with a statewide annual average temperature of 48.4°F, 4.6°F above the long-term (1895–2020) average. Warming has been concentrated in winter and spring, while summers have not warmed substantially, a feature characteristic of much of the Midwest. A lack of summer warming is reflected in a below average number of hot days since 1990 (Figure 2a) and no overall trend in warm nights (Figure 2b). The winter warming trend is reflected in a below average number of very cold nights since 1990 (Figure 2c) and reduced ice cover in the Great Lakes. The 2000–2021 annual average maximum ice coverage was about 47%, compared to the 1973–1999 average of 58%.
Figure 2
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Statewide annual precipitation has ranged from a low of 22.7 inches in 1930 to a high of 41.8 inches in 2019. The driest multiyear periods were in the 1930s and early 1960s and the wettest in the early 1950s, early 1990s, and 2010s (Figure 2d). The driest consecutive 5-year interval was 1930–1934, and the wettest was 2016–2020. The frequency of extreme precipitation events has increased. Multiyear averages for 2-inch extreme precipitation events for the 2010–2014 and 2015–2020 periods are the highest on record (Figure 3). Snowfall is common in the state but varies regionally. Due to their proximity to the Great Lakes, the south shore of Lake Superior in the Upper Peninsula and the eastern shore of Lake Michigan in the Lower Peninsula receive much more snowfall than the rest of the state. Parts of the Upper Peninsula receive more than 180 inches annually.
Water levels in the Great Lakes have fluctuated over a range of 3 to 6 feet since the late 19th century (Figure 4). Higher lake levels were generally noted in the late 19th century, the early 20th century, and the 1940s, 1950s, 1980s, and late 2010s. Lower lake levels were observed in the 1920s and 1930s and again in the 1960s. For Lake Michigan–Huron, lower levels occurred during the first decade of this century. Lake levels have risen rapidly since 2013, with the highest levels since 1886 observed in 2020.
Under a higher emissions pathway, historically unprecedented warming is projected during this century (Figure 1). Even under a lower emissions pathway, annual average temperatures are projected to most likely exceed historical record levels by the middle of this century. However, a large range of temperature increases is projected under both pathways, and under the lower pathway, a few projections are only slightly warmer than historical records. Extreme heat is a particular concern for Detroit and other urban areas, where high temperatures combined with high humidity can cause dangerous heat index values, a phenomenon known as the urban heat island effect. Higher spring temperatures will lengthen the growing season but also potentially increase the risk of spring freeze damage. In 2012, record-high March temperatures caused Michigan’s fruit trees to bloom early. When temperatures dropped back down to below freezing in April, the budding fruit crop was destroyed, causing exceptionally large monetary losses in the hundreds of millions of dollars.
Increases in precipitation are projected for Michigan, most likely during the winter and spring (Figure 5). The frequency and intensity of extreme precipitation are also projected to increase, potentially increasing the frequency and intensity of floods. Springtime flooding, in particular, could pose a threat to Michigan’s important agricultural industry by delaying planting and threatening yield losses.
The intensity of future droughts is projected to increase even if precipitation increases. Rising temperatures will increase evaporation rates and the rate of soil moisture loss. Thus, summer droughts, a natural part of Michigan’s climate, are likely to be more intense in the future.
Changes in seasonal and multiyear precipitation and increases in evaporation rates due to rising temperatures can affect water levels in the Great Lakes, causing serious environmental and socioeconomic impacts. During the 1980s, high lake levels resulted in the destruction of beaches, erosion of shorelines, and the flooding and destruction of near-shore structures. Low lake levels can affect the supply and quality of water, restrict shipping, and result in the loss of wetlands. Future changes in lake levels are uncertain and the subject of research. Reduced winter ice cover from warmer temperatures also leaves shores vulnerable to erosion and flooding.
